Gas treatment is well known, particularly treatment of combustion gas. Most commonly, combustion gas is desulfurized and/or treated in an absorber to remove carbon dioxide, typically with an amine solvent. Examples for such systems are described in U.S. Pat. No. 7,514,053 or in WO 2010/102877. These and all other extrinsic materials discussed herein are incorporated by reference in their entirety. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.
While these methods are often satisfactory for a particular purpose, it has not previously been appreciated that the amine solvent in a CO2 absorber may undergo undesirable reactions, and particularly formation of nitro-amine compounds, especially nitrosamine from contact with combustion gases containing NO2. NO and NO2 compounds formed during combustion of fossil fuels are removed in known processes including staged combustion, selective catalytic reduction (SCR), and selective non-catalytic reduction (SNCR). However, these processes which are used upstream of flue gas desulfurization equipment are not efficient enough to remove all the NOx in the flue gas. The residual NOx will therefore pass to the flue gas desulfurization and CO2 absorber. In this context, it should be noted that traditional flue gas desulfurization systems do not function effectively to reduce nitrogen compounds from combustion gases. This is in part because desulfurization systems often use reagents such as limestone, which is far too acidic to remove nitrogen oxides such as NO and NO2 from the gas.
It is generally known that NOx compounds are present in most combustion gases, where NO is most typically present at much higher rates than NO2. For example, a typical gas from combustion of coal may contain NOx gases of which 95% are NO and about 5% are NO2. This ratio is different when other fossil fuels such as gas or oil are combusted. Additionally, because NO is considered inert, it has not been appreciated that more NOx compounds should be removed from combustion gases. It has also not been appreciated that residual and relatively small amounts of NO2 may ultimately lead to undesirable reactions with amine solvents which result in the formation of nitro-amine compounds, most likely because the NO2 levels in typical combustion gases are relative small as compared to NO levels and reaction of NO2 as an acid gas with amines to form a heat stable amine salt is known.
Therefore, even though numerous treatment processes for combustion gases are known in the art there is still a need to provide methods and devices suitable for combustion gas treatment that will lead to a reduction of generation and release of secondary reaction products, nitro-amine compounds, especially nitrosamine, from an amine absorber.